1. Field of the Invention
This invention pertains to catheters for passage through a vasculature system. More particularly, this invention pertains to a novel construction of at least a segment of a catheter.
2. Description of the Prior Art
Catheters are widely used in medical treatment. A catheter is an elongated flexible member advanced through the vasculature system to a desired site. The catheter may be advanced over a previously inserted guide wire.
With the catheter in place, a wide variety of substances may be passed through the catheter to the site. For example, drugs may be moved through the catheter for site--specific drug delivery. Also, implements may be passed through the catheter. The catheter may also be used to remove fluids from the site. Still further, a catheter may be equipped with implements (e.g., balloon tips) for performing procedures (e.g., angioplasty) at the site.
Catheters have long been used in cardiovascular treatment. More recently, catheters are used in neurological procedures requiring advancement of the catheter through very narrow vessels. To accomplish these advances, a high degree of flexibility is desired. Also, catheters need very thin walls in order to retain an internal bore having as large a diameter as possible.
While advancing a catheter, a physician may twist a proximal end of the catheter in order to cause a corresponding twist of the distal end of the catheter (referred to as "torque transmission response"). A consistently reliable torque transmission response (e.g., a consistent one-to-one torque transmission response) is desired.
In designing catheters, it is desirable to provide a catheter which is kink resistant. Namely, a catheter typically is a tube with an internal bore of circular cross-section. When a catheter bends, it may be inclined to kink resulting in closure or geometric deformation of the circular bore. Such closure or deformation is undesirable. Further, in certain applications, the catheter may be subjected to high internal pressures (e.g., 300 psi). Such pressures tend to burst the catheter or expand the catheter geometry.
In neurological applications, catheters preferably have extremely flexible distal tips. While a high degree of flexibility is desired, flexibility should be attained while retaining burst strength and without undue sacrifice of torque transmission response.
In certain applications, the distal tip of a catheter may be shaped for unique purposes. For example, in treating an aneurysm, the distal tip may be shaped to have a radial projection so the tip more easily enters and remains in the aneurysm when reaching the site. A common practice is to shape the tip through steam application. The steam application softens the polymer lining at the tip permitting it to be bent and retain a bent shape following the steam application. Where the distal tip is supported by a traditional coil or braid construction, the tip may not adequately retain the bent shape since the coil or braid is inclined to resume its unbent shape against the resistance of the polymer.